This invention relates to a cyclone furnace for intensive treatment or combustion of finely ground mineral raw materials in dispergated state. The furnace according to the invention can be employed for processes in the building material industry, chemical industry or in the non-ferrous and inferrous metallurgy.
The up-to-date development of industrial applications of the methods of intensive conducting of flame processes with utilization of cyclone chambers has brought the formation of two basic groups of installations directed to intensive thermal processing of dispergated raw materials.
The first group constitute the so called cyclone melting chambers; the second group are called cyclone flame reactors.
The cyclone melting chamber consists of a vertical, mostly cylindrical cyclone chamber whereto jointly or through separate channels the fuel, the oxygen carrier, and the mineral raw material to be processed are supplied. The chamber forms an exclusive and in the technical sense a complete processing installation aimed at complete melting of the processed raw material, and of ash in case of combustion of ash-containing fuel.
In the cyclone melting chamber, as a result of tangential introduction of fuel and oxygen carrier a swirled stream of combustion products is generated. The dispergated raw material supplied into the same chamber and present therein is entrained by the stream, and enables it to maintain or in case of non-tangential supplying, also to assume a vortex motion. The result of the vortex motion and of polydispersion of the processed raw material is a segregation of its particles. The more coarse particles depositing on the cylindrical chamber wall are subjected to melting, and form a flowing down layer of the fusion, the remaining more fine particles, not having sufficient time to reach the wall of the chamber, are melted within the chamber space, and are discharged therefrom in the stream of exhaust gases. The fusion flowing down over the cylindrical chamber wall and the gaseous combustion products of the fuel, carrying the more fine non-separated particles of the fusion, leave the cyclone melting chamber through one common port arranged in the bottom of the chamber. The non-separated portion of the fusion, escaping with the exhaust gases to outside the room of the processing installation, gets partially deposited on the walls of precipitation chamber.
The cyclone flame reactors representing the second group of installations for thermal processing of raw materials, have the structure of an horizontally or vertically arranged cyclone chamber provided with a jet burner of complete combustion fitted tangentially to the chamber cover. The chamber is in its cylindrical wall provided with a connection with the raw material supply system. The jet burner connected with the supply system of fuel and of oxygen carrier, supplies the cyclone chamber with a stream of combustion gases by means of the heat where the processing of the raw material is realized.
A development of the construction of cyclone flame reactors consists therein that between the jet burner and the cyclone chamber a so-called mixing chamber is provided wherein the raw material is introduced. In the mixing chamber, the raw material is mixed with the stream of gases flowing out of the jet burner, and being carried by the stream it gets heated up, and together with the stream of gas enters through a tangential inlet into the cyclone chamber where it gets melted. The mechanism of course of the melting process of the raw material within the cyclone chamber of the cyclone flame reactor is analogical to that occurring in a cyclone melting chamber. The fusion depositing on the walls of a cyclone chamber being positioned for instance horizontally flows out through a special port made in the bottom of the chamber near to its contact edge with the cylindrical wall. The exhaust gases, however, flow out together with the particles of non-separated fusion through a port arranged centrically in the bottom of the cyclone chamber. In case of vertical position of the cyclone chamber, the fusion and gases are disposed through a common outlet also arranged in the bottom of the chamber.
From among the publications showing the above specified solutions as known the following can be mentioned:
J. A. Niefiedov et al.: Ciklonnaja plavka v cziernoj mietallurgii. Kiev, Tiechnika 1975; E. S. Frantov: Primienienie ciklonnogo principa w ogniewych tiechnologiczeskich processach. in: Wysokoforsirowannyje ogniewyje processy. Collective work under the redaction of M. A. Nadjarov. Moscow-Leningrad: Energia 1967 p. 164-177. Author's certificates of USSR No. 535448, F27B 15/00; No. 531008, F27B 15/02; No. 366330, F27B 15/00; U.S. Pat. No. 3,759,501, F27B 15/00 (Cyclonic smelting apparatus).
The disadvantages of known apparatus for intensive thermal treatment of raw materials are discussed hereinbelow.
In case of a cyclone melting chamber, a substantial disadvantage is that the process of combusting the fuel and the treating process of melting the raw material are conducted within the same space. In the common space, a mutual disturbance of the fuel combusting process and the raw material treating process occurs since the courses of both processes are ruled by essentially different principal laws. The cyclone melting chamber being sometimes similar to the cyclone fuel combustion chambers, especially to those employed in thermal power stations, concurrently with the increase of its overall dimensions becomes less and less effective in removal of detrimental effects of the mutual interferences of processes, making it possible to control the continuity of the process in course of operation of the installation, as well as achieving of other advantages both technical and economical. The disadvantages do not occur only in units having small overall dimensions, and thus showing a low output. The occurrence of mutual interferences of processes running within a cyclone melting chamber causes the process to operate at temperatures not exceeding 1600.degree. C., and that as a rule the capacity of melting chambers cannot exceed 5 t/h. Such low capacity does not fulfill the requirements of the industry. The calorific effect of combustion of liquid and gaseous fuels in cyclone melting chambers, due to interference of the combustion process and the treatment process is within the limits of 8-12.multidot.10.sup.6 kcal/m.sup.3.h. The industry, instead, looks for thermal units showing the combusting calorific effect of the order of 20-30.multidot.10.sup.6 kcal/m.sup.3.h. Certain treating processes requiring high temperatures, of 2000.degree. C. or more, can be realized advantageously only when the fuel is combusted with a calorific effect of 35-40.multidot.10.sup.6 kcal/m.sup.3.h.
On the other hand, the cyclone flame reactors eliminate the most significant disadvantage of cyclone melting chambers by employing of an outer jet burner, and contingently of a mixing chamber, but this aim is achieved by deflecting from the principle and from profitable effects of fuel consumption in the cyclone chamber. The most important feature of the cyclone process in the cyclone chamber is the ability to mix or to separate the substances in the process with high capacity, and the ability of to achieve high values of the coefficient of heat and mass exchange. Thus in this aspect, the cyclone flame reactors are even inferior to the cyclone melting chambers if they are featured with low capacities. The purposefulness of maintaining reasonable dimensional proportions of the jet burner and the mixing chamber and cyclone chamber causes that the heat released of the last usually not to exceed the value of 6.multidot.10.sup.6 kcal/m.sup.3.h. As a consequence thereof, as for cyclonic process, a low unitary capacity of the cyclone flame reactor results which for low-melting raw materials, is melting at the temperature up to 1300.degree. C., does not exceed 0.4 t/m.sup.3.h.
Another inconvenience of known installations for thermal processing of raw materials is the impossibility of using coal as a fuel. The ashes remaining after combustion thereof enter into the composition of the alloy produced in the treatment process. The cyclone reactor provided with a jet burner and being coal-fired in a particular way manifests the natural trend of coal to burn with a long flame, with low heat releases of the combustion chamber, not exceeding the value of 2.multidot.10.sup.6 kcal/m.sup.3.h. This phenomenon constitutes an insurmountable difficulty of correlating the coal jet burner with the cyclone chamber of the reactor. Finally, a common inconvenience both for cyclone melting chambers and the cyclone flame reactor is the low efficiency of separation of the fusion from the stream of gases leaving the cyclone chamber. Not more than 60% of the alloy produced in the cyclone chamber flows off into the processing apparatus. The remaining portion, however, being not the separated fusion, escapes from the chamber together with the exhaust gases. A cause of essential difficulties of to separate off this portion of the fusion from the gases beyond the space of the processing apparatus is the high dispersion ability. Also as a result of lower temperatures occurring therein, the fusion increases its viscosity and/or solidifies mostly on the walls of the precipitation chambers or discharge ducts forming difficult to remove accretions. The solidified fusion is as a rule not appropriate for processing with the fusion flowing out of the cyclone chamber, but requires another mode of utilizing or to return it to repeated melting. The removing of accretions and/or the recovery of fusion carried by the gases makes necessary to heat up the walls of the precipitation chambers by means of additional burners at temperatures higher than that of solidifying the fusion. This operation is accompanied by a considerable increase of the unitary heat consumption.
Finally, it should be mentioned that known installations for thermal treatment of mineral raw materials have a closely restricted application range, as they are employed only for melting raw materials. The combustion or sintering of mineral raw materials is not conducted in known melting installations.
The present invention is aimed at elimination of the disadvantages shown by the above presented cyclone apparatus, and thus providing uniform construction of the furnace with respect to the conditions of conducting the treatment process and the possibility of to employ the furnace in several branches industry as a universal design. In the design according to the invention, a separate cyclone chamber of fuel combustion is employed, provided with two-sided outlet of heating gases. The chamber operates essentially in an horizontal arrangement, whereby the profiled outlets for heating gases produced therein are made in non-cylindrical side walls of the chamber. The cyclone combustion chamber is provided with a system supplying energy-formative agents, situated in the middle of the entire length of the cylindrical wall of said chamber. The system comprises the duct of the oxygen carrier, arranged tangentially to the cylindrical wall of the chamber, further, in close vicinity of the duct, a device, preferably in form of a slot-type burner, introduces the fuel mix into the chamber, and a device for the burning, usually of a type of portable burner. The inlet of the device is arranged near to the periphery of the combustion chamber, parallel to the duct of the oxygen carrier. When using coal as fuel, and if the ash generated therefrom must not enter into the composition of the furnace product, the combustion chamber is additionally equipped with stub connections for discharging the molten ash outside. The stub connections for discharging the molten ash are located in the lower portion of the cylindrical wall of the combustion chamber in vicinity of the periphery of opposite non-cylindrical walls. The profiled outlets in the opposite non-cylindrical walls of the cyclone combustion chamber lead to cyclone reaction chambers wherein the mineral raw material on being mixed with heating gases is subject to proper thermal treatment. Each cyclone reaction chamber is in its upper part, in the centre of the cover, provided with the supply system for mineral raw material, and provided at the end with a concentric compression chamber connected with a compressed air source. The compression chamber operating according to the principle of injection, secures a steady down-directed flow of the raw material inside the cyclone reaction chamber. The vertical axis of the cyclone combustion chamber is displaced in relation to the vertical axis of the cyclone reaction chambers in such way that the heating gas streams flow from the combustion chamber almost tangentially to the walls of the reaction chambers and therein assume a vortex motion. The displacement of axes equals to 1/6 through 3/6 of the diameter of combustion chamber.
The cyclone reaction chambers in their narrowing lower part terminate with outflow openings simultaneously forming a connection with the precipitation chamber. The precipitation chamber forms an element closing the furnace structure from the bottom. The chamber is made in the form of a closed tank where through an extreme outflow opening in the roof the furnace product flows down from the cyclone reaction chambers. The outlet of the duct of exhaust gases is arranged between the outlet holes, in the middle of their distance. The gases are eventually separated from the non-gaseous particles of the furnace product. A symmetrical arrangement of the outlet holes in the roof in relation to the outlet of the duct of exhaust gases, improves the hydrodynamical characteristic of the precipitation chamber and unifies the conditions of separation of the fusion particles from streams flowing out of the reaction chambers. In order to discharge the non-gaseous portion of the furnace product, the precipitation chamber is in its bottom part provided with a drain. The axes of the duct of exhaust gases are situated in one common plane. Such an arrangement of the outlets advantageously influes the operation of the precipitation chamber because it allows utilization of the dynamic pressure of the gases flowing out of reaction chambers onto the bottom of the precipitation chamber to assist the outflow (gravitational) by the nature of the non-gaseous product from the furnace. Moreover, the drain has a decompressive connection with the duct of exhaust gases, in order to eliminate the effects of excessive dynamic pressure, manifesting itself in knocking out of a portion of gases.
If the final product is a fusion then the drain is connected with a fusion processing apparatus. In the case, however, of a sintered product, the precipitation chamber is over the drain connected with a duct collecting plant.
The walls of the furnace chambers, exposed from their inner sides to direct action of high temperatures and corrosive agents, are lined with a thin layer, not less than 12 mm thick, of mineral refractory fastened on known metal pins. The basic criterion of selection of the refractory is the linear thermal conductivity. Outside, however, the chambers are fitted with an hermetic casing for recirculation of a cooling agent. The hermetic casing is connected with a plant recovering the waste heat. Also the duct of exhaust gases led out of the precipitation chamber to recover the waste heat is connected with a utilization assembly, for instance a fluidization apparatus, appropriated for heating up the mineral raw material before supplying it to treatment in the furnace.
From among numerous advantageous effects of the invention the following are worthy to be mentioned. Due to employing cyclone combustion chambers with a two-sided outlet of heating gases, entirely complete combustion of combustible gases is achieved.
A pilot execution of the furnace according to the invention has obtained heated gas streams with the capacity of an order of 40.multidot.10.sup.6 kcal/m.sup.3.h, resulting in very high capacities of cyclone reaction chambers, which for low-melting raw materials, that is melting at temperatures up to 1400.degree. C., are expressed with a value of 1.2 t/m.sup.3.h, and for those melting at temperatures of about 2000.degree. C.--with the value of an order of 0.5 t/m.sup.3.h.
The cyclone combustion chamber according to the invention, is able to liberate very large amounts of heat energy in a relatively small chamber volume, and provides the possibility to conduct the treatment process at temperatures of an order of 2500.degree. C., with enrichment of the fuel mix with oxygen.